var p = prompt("请输入圆的半径");



var c =Math.PI;
p = Number(p);
if(!isNaN(p)){
    document.querySelector("#a").value =p;
    document.querySelector("#b").value =p*2*c;
    document.querySelector("#c").value =c*p*p;
}else {
    alert("请输入数字")
}


